The invention relates to an internal combustion engine with multi-joint crank drive and additional masses on articulated connecting rods of the multi-joint crank drive for damping free inertia force.
Internal combustion engines of this type are known for example from DE-A-102005054761, DE-A-102005054760, EP-A-1126144, JP-A-2004124775 or WO-A-2007057149 and are often referred to as internal combustion engines with variable or changeable compression ratio, because the compression ratio can be changed by rotating the eccentric shaft.
In these internal combustion engines the multi-joint crank drive includes beside the eccentric shaft a number of coupling members which corresponds to the number of the cylinders, which coupling members are each rotatably supported on crank pins of the crankshaft and have two arms which protrude over the crankshaft toward opposite sides and are provided at their end with a pivot joint. One of the pivot joints serves for pivotally connecting a piston rod which connects a piston of the internal combustion engine with the crankshaft via the coupling member, while the other pivot joint serves for pivotally connecting a so called articulated connecting rod which is rotatably supported with its other end on a crank pin of the eccentric shaft.
Internal combustion engines of the above mentioned type are further known for example from EP-B-1359303, EP-A-1760290, EP-A-1760289 and U.S. Pat. No. 4,517,931. In these internal combustion engines which are often referred to as internal combustion engines with extended expansion, the eccentric shaft is driven with half the rotational speed of the crankshaft.
In all of these internal combustion engines free first and second-order inertia forces are caused by oscillating masses which inertia forces change with the crank angle. While the first order inertia forces are compensated by compensating weights on the crankshaft and the crank sequence of the crankshaft can be compensated, the free second-order inertia forces cannot be fully compensated in known internal combustion engines in spite of a broad spectrum of different measures. For this reason, internal combustion engines of the above mentioned type are inferior with regard to the running smoothness and running characteristics to conventional internal combustion engines without multi-joint crank drive in which the compensation of second inertia forces occurs often by means of two counter rotating compensation shafts which are driven with double the rotational speed as the crankshaft. However, these measures cannot readily be applied to internal combustion engines with multi-joint crank drive because in this case, on one hand the generated inertia forces do not have a purely oscillating but rather rotating course, and on the other hand, the friction losses of the multi-joint crank drive are already higher than the friction losses of conventional internal combustion engines and would be increased to an unacceptable degree by the additional friction losses of two compensating shafts.
In order to avoid this, the applicant has already proposed in the still unpublished German Patent application 10 2010 004 589 to provide only a single compensation shaft in internal combustion engines of the above mentioned type for damping second-order inertia forces with which these inertia forces can be almost completely compensated.
Taking the above into account, the invention is based on the object to improve an internal combustion engine of the above mentioned type in that the second-order inertia forces can be compensated even better without significant increase of the friction losses, the required construction space, the weight of the multi-joint crank drive or the support forces in the bearings of the crankshaft.